cps-ir: Support foreign code.

pkg/compiler/lib/src/tree_ir/tree_ir_tracer.dart

Index: pkg/compiler/lib/src/tree_ir/tree_ir_tracer.dart
diff --git a/pkg/compiler/lib/src/tree_ir/tree_ir_tracer.dart b/pkg/compiler/lib/src/tree_ir/tree_ir_tracer.dart
index fee1dd7adcb33d52b63659533e63a44f2bcabc96..90c0b69577ac486b89976498474657cb73a978eb 100644
--- a/pkg/compiler/lib/src/tree_ir/tree_ir_tracer.dart
+++ b/pkg/compiler/lib/src/tree_ir/tree_ir_tracer.dart
@@ -172,6 +172,10 @@ class BlockCollector extends StatementVisitor {
     _addStatement(node);
     visitStatement(node.next);
   }
+
+  visitForeignStatement(ForeignStatement node) {
+    _addStatement(node);
+  }
 }
 
 class TreeTracer extends TracerUtil with StatementVisitor {
@@ -321,6 +325,11 @@ class TreeTracer extends TracerUtil with StatementVisitor {
   String expr(Expression e) {
     return e.accept(new SubexpressionVisitor(names));
   }
+
+  @override
+  visitForeignStatement(ForeignStatement node) {
+    printStatement(null, 'foreign');
+  }
 }
 
 class SubexpressionVisitor extends ExpressionVisitor<String> {
@@ -511,6 +520,12 @@ class SubexpressionVisitor extends ExpressionVisitor<String> {
   }
 
   @override
+  String visitForeignExpression(ForeignExpression node) {
+    String arguments = node.arguments.map(visitExpression).join(', ');
+    return 'Foreign "${node.codeTemplate}"($arguments)';
+  }
+
+  @override
   String visitApplyBuiltinOperator(ApplyBuiltinOperator node) {
     String args = node.arguments.map(visitExpression).join(', ');
     return 'ApplyBuiltinOperator ${node.operator} ($args)';